Effect of α-Al2O3 content on microstructures, mechanical properties and purification efficiency on molten steel of MgO-based filters

In this study, five sets of MgO-based ceramic filters were prepared using porous MgO powder and a-Al2O3 micropowder as raw materials. The effect of a-Al2O3 content on the microstructures, mechanical properties and purification efficiency of MgO-based filters were investigated via SEM, EDS, and immersion test in molten steel, etc. The results indicate that the reactive sintering between a-Al2O3 and MgO promoted the formation and growth of neck connections of magnesium aluminate spinel between grains, increased the density of the filter skeleton, and decreased the pore size inside the skeleton. The higher density and smaller pore size of the skeleton, as well as the neck connection of spinel and crack deflection effect caused by magnesium aluminate spinel, comprehensively improved the strength and thermal shock resistance of MgO-based ceramic filters. Furthermore, the results from the immersion test in molten steel revealed that an appropriate amount of high-temperature liquid phase, smaller pore size, and in-situ generated spinel were beneficial for the filters to adsorb dissolved aluminum, dissolved oxygen, alumina inclusions, and secondary spinel inclusions in the steel. The filter with 20 wt% a-Al2O3 had the best overall performance with a compressive strength of 2.35 MPa, a compressive strength after thermal shock test of 1.91 MPa and an efficiency of 77.3% in reducing the total oxygen content of the steel.